Filter cigarettes



P 10, 19.63 w. R. MAHONEY ETAL. 7 3,103,220

FILTER CIGARETTES Filed June 12, 1959 2 Sheets-Sheet 1 Tow U- 1113- 6 15 E y P 1963 w. R. MAHONEY ETAL 3,103,220

FILTER CIGARETTES 2 Sheets$heet 2 Filed June 12, 1959 3,103,220 FILTER CIGARETTES William R. Mahoney, Richard E. St. Pierre, and Donald 'LDnnlap, Charlotte, N.C., assignors to Cclanese Cor:- poration of America, New York, N.Y., a corporation of Delaware Filed June 12, 1959, Ser. No. 820,941 9 Claims. (Cl. 131-40) The present invention relates to a voluminous mass or tow of filamentary material suited for making cigarette filters and other uses.

This application is a continuation-in-part of application Serial No. 714,634, filed February 11, 1958, now U.S. Patent No. 3,032,829. 1

Voluminous or bulked filamentary tows or bundles of filaments are useful for a variety of purposes such as making ellicient cigarette filters, making wool-like or bulky textiles, and the like. Cigarette filters are generally formed of a multiplicity of crimped filaments, starting with a cr-imped tow or bundle of several thousand continuous filaments. As, received from the tow producer, the filaments may bemore or less adheredto each other with the crests and vales of adjacent filaments in registry. The tow is passed through an air spreader, is fed by driven rolls through a chamber in which plasticizer is applied,;'-and it is thereafter condensed to equal approximately the cross-sectional area of a cigarette. The condensed mass is formed into a coherent structure such as by wrapping in paper land/or curing and is cut into suitable lengths for incorporation into cigarettes.

In commercial operation is has been found that the filters so produced'are not all identical in their filtering action. Specifically, it has been found that the filters occasionally differ in weight, in filtering efficiency and in the ease of draw, i.e. resistance to gas flow. In addition, after smoking many filters show uneven darkening which indicates non-uniform passage of smoke therethrfough, the darkened areas identifying zones through which the smoke was .preferentially drawn;

For producing bulky textiles, a continuous filament yarn may be passed through a turbulent zone of pres- .surize'd fluid, beingdischarged therefrom along with the fluid. The yarn is taken up at a slower speed than it is fed andis characterized by high bulk. While the product is generally satisfactory,'the process entails the use of large volumes of pressurized fluid.

It is accordingly an object of the present invention to provide different types ofbulked or voluminous tows or bundles of filaments. v

7 It is a further object of the invention to provide improved voluminized tows and improved cigarette filters produced therefrom.

Another object is to provide procedures for producing such improved vol-uminized tows.

Other objects and advantages will be apparent from the following detailed description and claims.

Our investigations have revealed that a major cause of irregularities in the filter tips and their filtration characteristics can be traced to the procedure for opening of the tow. Specifically, in the crimping of the tow all of the filaments are simultaneously acted upon and it will be found that the crimps of adjacent filaments are in registry; if such crimp registration is not done away with there will be channels in the filter through which smoke can pass without contacting any filament surface. produced, the tow may contain individual filaments or groups of filaments which do not extend longitudinally but rather which extend at an appreciable angle transversely of the tow. In'processing, these transversely extending filaments or cross-overs tend to prevent those filaments which they overlie from being spread apart laterally.

iU t dstat s Patent In addition, as

.clined in different directions.

1 counterclockwise.

If a tow has not been evenly crimped initially, the tow opening procedure may result in uneven application of plasticizer and this in turn may result in uneven density with channeling of smoke through the filter.

In accordance with one aspect of the present invention the tow is opened by passage'over a ridge which is inclined to the path of movement of the tow. Conveniently the tow is passed between several pairs of opposed ridges, at least one ridge of each pair being inclined to the path of movement of the tow, preferably both being in- This can readily be achieved by passage between -a pair of opposed ridged surfaces, the ridges of one surface being displaced laterally relative to the ridges of the other surface, thereby laterally displacing some of the filaments relative to other of the filaments and thus opening the tow. Preferably the ridged surfaces are constituted by a pair of opposed grooved or ridged cylindrical rolls which are positioned close to one another and rotate upon passage of tow therebetween. The surfaces are so formed that the ridges of one surface will not always be in registry with the grooves of the other surface.

A suitable configuration of ridges is created by forming 'a helical thread in an elastic, e.g. rubber, or elastic-surfaced cylindrical roll. Advantageou'sly both rolls are threaded'in the same direction so that as they rotatein opposite directions the ridges of one roll will not be in permanent registry with the grooves of the other roll. By way of illustration, at a given time a point on one ridge of oneroll will contact some point on a ridge of the other roll and as the tow advances the rolls will rotate and the points on the rolls where they were previously in contact will be displaced laterally relative to each other.

If the opposed rolls are oppositely threaded, then their pitches, circumferences or rotational speeds should be different so that there will not be permanent registry between the ridges and grooves of the-rolls, i.e. so that points on both rolls where they are in contact will be laterally displaced relative to each other.

Each helical roll will tend to displace the tow laterally in the direction of advance of the helix, considering its direction of rotation, e.g. if a helically grooved roll, on which the thread as viewed from one end advances in clockwise direction, is rotated in counterclockwise direction a tow contacting the roll will tend to be displaced away from theviewer. Where the other roll is similarly threaded but rotates in opposite direction the tow will tend to be displaced toward the viewer. Both of these simultaneously acting tendencies further aid in opening the tow.

Conveniently, each roll is threaded from one end to its'center in one direction, e.g. clockwise, and from its other end tov its center in the opposite direction, e.g. Two such rolls are assembled with .their clockwise-threaded sections opposite each other and with their counterclockwise-threaded sections opposite each other. One of the rolls will thus tend to condense laterally a tow fed near its middle while the other roll will tend to expand the tow laterally. V

The ridged opening surfaces can be incorporated directly into existing apparatus for forming cigarette filters from tow, including an air spreader, if desired. After passing between the ridged surfaces the tow is passed between a pair of braking rolls and then between a pair of driven rolls. The tow is thus tensioned between thedriven and'braking rolls, the tension temporarily pulling out the crimp and making it more regular upon subsequent relaxation. If desired, the braking rolls may be omitted, their functionbeing performed by the ridged opening'surfaces. Following passage between the driven rolls, which operate at constant speed, the tow is-advmtageously passed through an air spreader, sprayed in relaxed condition with a plasticizing agent and conveyed to conventional condensing equipment to be formed into rods for incorporation into cigarettes as filter plugs.

In place of two opposed helically ridged cylindrical surfaces, one of the surfaces can be provided with circular or elliptical ridges. Alternatively, both surfaces may be provided with elliptical rings which are either oppositely canted or arranged at different angles relative to their respective axes so that the ridges on one cylinder will not always lie in registry with the grooves of the other cylinder. A similar efiect will be achieved using one cylinder with circular rings and another with elliptical r1ngs.

In another embodiment, in place of providing the ridges on a pair of cylindrical surfaces, one or both of the surfaces may be fiat and the ridges can be shaped as they would appear if the rubber covering were removed from the cylindrical roll and were laid flat.

The ridges of one of the opposed surfaces can be registered with the grooves of the other surface in one position but, as noted, should not be in permanent registration. Thus, circular rings on both cylindrical rolls or straight parallel ridges on both opposed fiat surfaces can be employed provided the registry is interrupted as by oscillating one or both surfaces laterally out of phase with or in opposite direction to the other surface. While circular rings are parallel to the direction of advance of the tow, such oscillation effectively inclines the rings so as to produce the efiect of elliptical rings.

.The tow is preferably composed of a plurality of crimped continuous filaments of an organic derivative of cellulose, e.g. esters or ethers of cellulose such as cellulose acetate, cellulose propionate, cellulose acetate propionate, highy esterified cellulose containing less than 0.29 free hydroxyl group per anhydroglucose unit such as cellulose triacetate, and the like. Other filamentary materials such as rayon (regenerated cellulose), linear superpolyamides such as nylon-6 and nylon-66, linear polyesters, acrylonitrile polymers and copolymers, and the like, can also be employed. I

'The identity of the plasticizer will of course depend upon the composition of the tow. With cellulose acetate there may be employed triethyl citrate, dimethoxy ethyl phthalate and methyl phthalyl ethyl glycolate but glycerol triacetate (triacetin) is preferred.

With tows opened in conventional manner there will 1 still be appreciable registry among adjacent crimped filaments which is aggravated at low deniers. By con trast, in accordance with the present invention the denier of the individual filament may be as little as 2, although 17 or more is also possible. Even with small deniers below about 7 the extensive opening and deregistry prevents channeling of the smoke so that such low deniers are permissible. At the same time the low denier filaments provide a greater surface area. In addition, they produce firm filters which can be cured with less plasticizer with attendant savings in time and material. Even at low plasticizer levels the novel plugs will be as firm as conventional plugs having much greater plasticizer content. Firmness is measured by permitting a 4-ounce load knife edge to rest transversely of a paper-wrapped filter plug for 10 seconds. .The percent firmness is 100 times the height of the plug at the base of the depression divided by the original diameter of the plug. The percent compressibility is 100-percent firmness. Generally the firmness of a satisfactory cigarette filter comprising a cured plug is at least about 75% and preferably at least about 80%. Whereas with conventional plugs this requires a relatively high plasticizer content, with the novel plugs equal firmness can be achieved at plasticizer contents of about 10% and preferably 7% or even less.

The filtration efficiencies of filters prepared from the novel tow are greater than those of filters prepared from conventionally opened tow. As a corollary, the efiiciency of conventional filters can be duplicated at lower plug weights and/or with less resistance to draw, i.e. lower pressuredrop. The total number of filaments may be as much as 120,000 or more, preferably about 3,000 to 60,000, and the total denier may be about 40,000 to 120,000 or more, preferably about 60,000 to 80,000.

The number of crimps per inch in the tow can range up to about 20 but preferably averages between about 4 and 12. After leaving the driven rolls the tow is still crimped but is about 10 to 200%, and preferably 50 to longer than initially, i.e. the tow has been stretched so that the distance between the crests of adjacent crimps has been increased and the amplitude reduced. In addition, the crimps are deregistered and more regular than initially.

With tows opened in conventional manner filters produced therefrom will exhibit reduced pressure drops and filtration efi'iciences as the weight is decreased for a given tow specification, i.e. as for a given number of filaments the stretch is increased to decrease the weight of tow in a plug of given length. If the plug weight is decreased too much, however, a limp useless plug will result. In accordance with the present invention it has also been found that the pressure drop and smoke removal or filtration efiiciency generally decrease with decrease in the plug weight. Surprisingly, however, a plug weight is reached which when further decreased produces an increased pressure drop and smoke removal efficiency. The exact value for this critical weight will vary, depending upon the constitution of the tow, i.e. crimp, denier per filament and total denier, but generally lies in the neighborhood of about 0.18 gram per 15 mm.

In accordance with another aspect of the invention, the tow fed to the ridged surface may comprise relatively few filaments. The t-ow may be fed and taken up as a yarn of little or no twist, without having previously been partially opened. The yarn is voluminized or bulked in a manner somewhat resembling crimping, except that the filaments are not likely adhered to one another as when employing a conventional stufling box crimper. The voluminizing is even and regular with no filament extending straight for any appreciable distance. The degree of voluminizi-ng will depend upon the arrangement of the ridges.

In accordance with another aspect of the invention, the opened voluminous tow may be employed as a bottle wadd-ing, padding or stuffing material, in which capacities its high bulk results in decreased Weight and material expense. The use of continuous filament material also facilitates handling since there are no short lengths of staple fibers flying about and adhering electrostatically to equipment. In addition, desired quantities can readily be severed with accuracy since the weight per 'unit length of the opened tow is quite uniform. Storage and shipping costs are also reduced since the tow can be handled in dense bales and will be opened only immediately prior to use.

A stuffing material can also be produced from opened tow which, advantageously Without pl-asticization, is continuously vformed into a paper-wrapped rod and severed into lengths which may be the same as or difi'erent from the length of cigarette filter plugs. The ends of such plugs are treated with solvent, plasticizer or heat to fuse the fibers and the wrapping is then removed to allow the coherent mass to balloon laterally.

The invention will now be described more fully with reference to the accompanying drawing, wherein:

FIG. 1 is a schematic elevation of a tow opening apparatus in accordance with the present invention;

FIG. 2 is a schematic elevation of a modified tow opening apparatus;

'FIG. 3 is a lateral elevation of the helically threaded tow opening rolls of FIG. -1;

FIG. 4 is a section through a portion of one of the rolls taken along line 44 of FIG. 3;

.5, FIG. is a lateral elevation of another pair of tow opening rolls which can be employed in the practice of the present invention;

FIG. 6 is an elevation of a pair of ridged flat plates which can be substituted for the ridged. rolls: of 'FIG. 1; FIG. 7 is a plan View of one of the plates of FIG. 6;

FIG. 8 is a perspective view of a cigarette, with the wrapper partially torn away, including a novel filter;

FIG. 9'-is a view of a yarn produced in accordance with I the invention; U H

FIG. 10 is a schematic perspective view of an apparatus for treating the opened tow; i

FI G., ll is a perspective view of a bottle containing .a short length of the product of the appa'ratusof FIG.10.

Referring now more particularly to the drawing wherein like numerals have reference to the same element, in

FIG. 1 there is shown a bale 11 of a multifilament tow 12, which tow is passed through an air spreader 13 comprising a pair of spaced plates provided on their oppose-d faces with longitudinal slits through which compressed air is directed against the tow.

From the air spreader 13 the tow 12 is drawn between rolls 14, 14 each of which is elastically surfaced as at 15. 'The rol-ls 14 have the configuration shown in FIGS. 3

and 4 and described more fully hereinafter. A. yoke 16 determines the spacing between the rolls 14 and includes means .for oscillating the rolls 14in opposite directions perpendicular to the plane of the drawing althoughpreferably the rolls are not oscillated but are merely supported for rotation. The tow 1 2 is then drawn between rubber braking rolls 17 which may be driven or which may be idly mounted for rotation.

The tow 12 then passes to posit'vely driven rolls 18 which are also elastically surfaced and supply the force necessary to draw thetow along. These rolls 18 operate at a constant speed attuned to the operating speed of the cigarette making machinery. It the braking rolls 17 are positively driven, they are driven at a slower speed than rolls 18 so as to exert a braking action on the tow.

The tow passes through another air spreader 19 and enters a plasticizin'g chamber 20 wherein there is provided a mist of plasticizer. The plasticized tow upon emerging from chamber 20 is now in condition for passage to rodforming equipment (not shown) in order to be formed continuously into cigarette filter plugs. Although the tow 12 is now relaxed the spacing between crests of adjacent crimps is greater than it was initially.

Filter rods and plugs formed from the tow are charvacterizedby uniformity in weight, filtering characteristics and density. Smoke passing therethrough is not channeled as can be seen from the absence of unevenly discolored areas at the end of the filter. The plugs are firm and the paper wrapping does not wrinkle, indicating a tight uniform packing. ,These advantages are noted even moved closer toward each speed of driven rolls 18 will resultin a tow having the I desired percent crimp, i.e. the rolls 18 are driven atthe selected speed and the rolls 14-,are moved toward each other until the tow emerging from between rolls 18 has the desired properties; The force of rolls .17. against each other may also be varicd'to avoid unduly increasing 'the spacing between rclls ld'whichimight reduce the opening action. The rolls14 may also be reciprocated in axial direction to aid in opening.

The rolls 14 rotate in the direction indicated by the arrows and it will be seen that the upper roll will tend passed between ridged rolls 14.

but little registry in the crimps of adjacent filaments.

conveniences attending such loose particles.

to reduce the width of the tow passing therebetween while the lower roll will tend to increase' thewidth of the tow. In practice it has been .tound'that with identical rolls grooved as shown the lower roll apparently exerts a greater influence so that there is a net increase in width of the The modified apparatus shown in-FIG. 2 is identical with thatof FIG. 1 except that thebrakin-g rolls 17 have been omitted. In this embodiment the grooved r0lls'14 take over thel braking function to control the stretchingv of the tow. Control over the uniformity of crimp, i.e. uniformity of tow density in longitudinal direction of the tow, is less exact but a regularly crimped tow is initially employed the product will be almost as uniform as that produced by the apparatus of FIG. 1, whereas the apparatus of FIG. 1 will giveexcellent results with tows which are regularly crimped, e.g. by toothed gear wheels, as well as with more randomly crim-ped tow.-

In. placeof a pair of rolls 14 whichare helically threaded in opposite direction from each end, each roll maybe threaded only in one direction. Alternatively, as shown in :FIG. 5, one roll 21 may be provided with parvallel'circular ridges or rings 22 each extending in a plane perpendicular to the axis of the roll 21 while the other rol123 is provided with parallel elliptical ridges or rings 24- each extending in a plane inclined relative tothe axis of roll 23. It is apparent that upon rotation there will be relative lateral movement between the-ridges 22 and the ridges 24; i This will also be. achieved if either roll 21.0r 23 is used in conjunction with one roll 14, if two rolls 23 are used with their ridges inclined in opposite directions, if two rolls 21 are used and one is reciprocated laterally relative to the other, etc.

FIG. 6 shows a pair of plates 25 which can be substituted for the rolls 14. In use the plates may be reciprocated laterally but they are preferably stationary. Each plat 2'25 hasa ridged surface and as can be seen in FIG. 7

the surface has the appearance whioh woul-d result from cutting rubber covering 15 -of roll 14 parallel to the roll axis and flattening out the covering.

'In FIG. 8 there is shown a. cigarette comprising an outer paper wrapping 26 enclosing tobacco- 27 and a filterco'm'posed of a paper Wrapper 28 surrounding filaments 29. The filter comprising wrapper 28 and filaments 29 may be made by wrapping tow .12 with paper in conventional manner as it leaves plasticizer chamber 20 (FIGS. 1 and 2), cutting it into predetermined lengths v (not shown) and curing. To the naked eye the filterwill look the same as conventional filters, but it will feel more firm than conventional filters of equal filament and plasticizerlcontent. If the filter is broken apart, or if the tow is examined as it leaves rolls 18 it will be apparent that the towis more voluminous than tows of the same number of filaments and total denier which have not been In addition, there will be The yarn 30 shown in FIG. 9 comprises many filaments \'vl1 ich appear to be volurniuized in more or less registry.

The filaments, however, are individual rather than lightly adhered as when crimped in conventional manner.

In place of being plasticized and formed-into cigarette filter plugs, as shown 'in FIG. l0,the opened tow 31 can be cut by cutter 32 into predetermined lengths 33 suited for stufling, padding or bottle wadding. Because of their open structure, lengths 33 fill out any space into which packed. They are free of short fibers which can work their wayloose, thereby eliminating, the problems and in- In addition, they are clean, highly absorbent and inert. FIG. 11 showssuc-h a mass 33 stufied into abottle 34 containing material such as 'aspirins 35, themass 33 keeping the aspirins from moving about or becoming soggy and losing their individual shapes or identities.-

7 EXAMPLE I (a) Using the apparatus shown in FIG. 1, an 80,000 denier tow of 20,000 cellulose acetate continuous filaments, averaging 8 crimps per inch, is passing through air spreader 13 and is subjected t compressed air at 3 p.s.i.-g. The tow passes between grooved rolls 14 which are 14 inches long and 5.5 inches in diameter, eighteen helical threads per inch being cut about inch deep into the rubber covering. Next, the tow passes between braking rolls 17, idly mounted for rotation and forced against each other sufficiently hard to require a force of 15 pounds to pull the tow manually therethrou-gh. Driven rolls 18' are rotated at a peripheral speed of 37.25 yards per minute and the tow picks up 7% of its weight of triacetin in chamber 20. The tow leaving chamber 20 is wrapped with paper on conventional cigarette making equipment and cut into 15 mm. lengths which are cured for 2.4 hours at room temperature. One hundred such plugs are tested for weight, pressure drop and smoke removal efficiency. The pressure drop is the suction necessary to maintain a flow rate of 17.5 cc. of air per second through the plug, not incorporated into a cigarette. In determining smoke removal efiiciency, 12 puffs of 35 cc., i.e. 2 seconds of puffing, are drawn from a lit cigarette through the filter and through a trap having on its bottom a sintered glass disk. 2 grams of sifted alpha cellulose are placed on the disk, producing a pressure drop of about 5 centimeters of water. The trap is immersed half way in a Dry Iceacetone bath. The formula for the smoke removal efliciency is as follows:

A weight of filters Percent efiimency=A wt. of filters+A wt. of trap EXAMPLE 11 (a) The process of Example I(b) is repeated with a tow made up of 21,000 of the same filaments. The plugs weigh 0.18 8 gram, have a pressure drop of 62 .1 mm. H 0 and a smoke removal efliciency of 15.1%.

(b) Inserting the grooved rolls into the process of Example II(a) and increasing the stretch, the plugs weigh 8% less. While the pressure drop of the well-opened tow goes up 4%, the smoke removal efiiciency goes up 42%.

While the extensive opening of the tow resulted in a somewhat increased pressure drop for the novel filters, it will be noted that. the percent increase in smoke removal efficiency exceeded the percent increase in pressure drop 100=percent increase) EXAMPLE III The process of Example I is repeated with a tow of 40,000 filaments each of 2 denier. The speed of rolls 18 is varied in successive runs to produce plugs of varying weight. The results of tests on weight, pressure drop and smoke removal efiiciency of 13 mm. plugs are given in the following table. The weight in grams set forth in the table below is for a constant volume of about 0.649 cubic centimeter which is the standard cigarette filter volume,

Table Pressure Smoke Run Weight, Drop, Removal, Density Grams mm. H1O percent (gms/cc.)

A cigarette filter plug has a standard circumference of 25 millimeters. The following graph depicts the smokeremoval efliciency of the filter plugs of Example II with respect to filter-plug density.

Smoke-Removal Efficiency, Percent Density, Grams/cc.

It can be seen that as the plug weight decreases initially, the pressure drop and smoke removal efiiciency also decrease. In reducing the plug weight going from run 3 to run 4 surprisingly the smoke removal efiiciency increases. In going on to run 5 it is found that although the weight is less both the pressure drop and smoke removal efliciency are greater than in run 3. This effect is further evidenced in run 6.

Similarly a consideration of the graph points out that as the density decreases, the smoke-removal efficiency decreases but that this reaches a minimum and thereafter a decrease in filter-plug density results in an increase in smoke-removal efficiency.

EXAMPLE IV Using the grooved rolls shown in FIG. 1 a cellulose acetate yarn composed of 240 4-denier filaments united with 4.5 2 turns per inch are pulled between the grooved rolls by rolls driven at 37 .25 yards per minute, emerging from the driven rolls as a crimped yarn.

EXAMPLE V The same tow used in Example I, after leaving rolls 18, is cut into 1 centimeter lengths used as a Wadding in medicine bottles. 5

It is to be understood that the foregoing detailed description is given merely by way of illustration and that many variations may be made therein without departing from the spirit of our invention.

Having described our invention what we desire to secure by Letters Patent is:

l. A cigarette having incorporated therein as a filter a plug of substantially uniform cross-sectional density comprising crimped cellulose acetate continuous filaments carrying less than about of a plasticizer based on the Weight of the filaments serving to bond said filaments to one another at their contact points, said plug having a firmness of at least about 75%, a density less than about 0.23 gram per cubic centimeter, and a smoke removal efliciency of at least about 2. A cigarette having incorporated therein as a filter a plug of substantially uniform cross-sectional density comprising about 3,000 to 120,000 crimped continuous cellulose acetate filaments of less than about 25 denier each, said filaments carrying less than about 10% of a plasticizer based on the weight of cellulose acetate serving to bond said filaments to one another at their contact points, having a firmness of at least about 80%, having a smoke removal eificiency of at least about and having a density less than 0.23 gram per cubic centimeter.

3. A plug of substantially uniform cross-sectional density for cigarette filters comprising crimped continuous cellulose acetate filaments carrying less than about 10% of a plasticizer based on the weight of the filaments serving to bond said filaments to one another at their contact points, said plug having a firmness of at least about 75 a density less than about 0.23 gram per cubic centimeter, and a smoke removal efficiency of at least about 15%. i

4. A plug of substantially uniform cross-sectional density according to claim 3, including about 3,000 to 120,- 000 filaments of less than about denier each.

. 5. A plug of substantially uniform cross-sectional density according to claim 3, wherein said filaments comprise cellulose acetate.

6. A plug of substantially uniform cross-sectional density for cigarette filters comprising about 3,000 to 120,000 crimped, synthetic thermoplastic continuous fil ments of less than about 7 denier each said filaments carrying plasticizer material serving to bind said filaments to eachother at their contact-points, said plug having a firmness of at least about a density less than about 0.23 gram per cubic centimeter, and a smoke removal eficienoy of at least about 15 7. A plug of substantially uniform cross-sectional density for cigarette filters comprising crimped, cellulose acetate continuous filaments of less than about 7 denier each carrying less than about 10% of a plasticizer based on the weight of the filaments serving to bond said filaments to one another at their contact points, said plug having a firmness of at least about 75 a density of less than about 0.23 gram per cubic centimeter, and a smoke removal efficiency of at least about 15%.

8. A plug of substantially uniform cross-sectional density for cigarette filters comprising about 3,000 to 120,000 crirnped, synthetic thermoplastic continuous filaments of less than about 7 denier each carrying less than about 10% of a plasticizer based on the weight of the filaments serving to bond said filaments to one another at their contact points, said plug having a firmness of at least about 75%, a density less than about 0.23 gram per cubic centimeter, and a smoke removal efiiciency of at least about 15%. r

9. A plug of substantially uniform cross-sectional density for cigarette filters comprising about 3,000 to 120,000 crimped, continuous cellulose acetate filaments of less than about 25 denier each, said filaments carry less than about 10% of a plasticizer based on the weight of cellulose acetate serving to bond said filaments to one another at their contact points, having a firmness of at least about having a smoke removal efiiciency of at least about 20% and having a density less than 0.23 gram per cubic centimeter.

References Cited in the file of this patent UNITED STATES PATENTS 2,222,042 Nitardy June 16, 1937 2,476,582 Browne et al July 19, 1949 2,655,259 Davoren Oct. 13, 1953 2,750,653 White June 19, 1956 2,789,563 Taylor et al Apr. 23, 1957 2,794,239 Crawford et a1. June 4, 1957 2,804,078 Satfir Aug. 27, 1957 2,805,671 Hackney et al. Sept. 10', 1957 2,881,771 Touey Apr. 14, 1959 

1. A CIGARETTE HAVING INCORPORATED THEREIN AS A FILTER A PLUG OF SUBSTANTIALLY UNIFORM CROSS-SECTIONAL DENSITY COMPRISING CRIMPED CELLULOSE ACETATE CONTINUOUS FILAMENTS CARRYING LESS THAN ABOUT 10% OF A PLASTICIZER BASED ON 